[room271]

Persistent data structures allow for the appearance of cloning (you have a new thing) but are much more efficient behind the scenes (you don't actually copy everything). So if you find yourself doing a lot of defensive cloning, then Mori or this library would probably be a lot faster for you.

[nawitus]

Absolutely! If anyone is reading this, I recommend Eric Lippert's 11 part series on immutability in C#. The concept apply everywhere, of course.

http://blogs.msdn.com/b/ericlippert/archive/2007/11/13/immut...